Hybrid corn variety 2643391

ABSTRACT

The invention provides seed and plants of the hybrid corn variety designated 2643391. The invention thus relates to the plants, seeds and tissue cultures of the variety 2643391, and to methods for producing a corn plant produced by crossing a corn plant of variety 2643391 with itself or with another corn plant, such as a plant of another variety. The invention further relates to genetic complements of plants of variety 2643391.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims a priority based on provisional application61/665,548 which was filed in the U.S. Patent and Trademark Office onJun. 28, 2012, the entire disclosure of which is hereby incorporated byreference.

FIELD OF THE INVENTION

This invention is in the field of corn breeding. In particular, theinvention relates to a hybrid corn variety designated 2643391 thatincludes plants and seeds of hybrid corn variety.

BACKGROUND OF THE INVENTION

Corn (Zea mays L.) is the most important and abundant crop produced inthe United States. Corn is used as human food, livestock feed, and as anindustrial raw material. The food uses of corn include kernels for humanconsumption, dry milling products such as grits, meal and flour, and wetmilling products such as corn starch, corn syrups, and dextrose. Cornoil recovered from corn germ is a by-product of both dry and wet millingindustries. Both grain and non-grain portions of corn plants are usedextensively as livestock feed, primarily for beef cattle, dairy cattle,hogs, and poultry.

Corn is used to produce ethanol while corn starch and flour are used inthe paper and textile industries. Corn is also used in adhesives,building materials, foundry binders, laundry starches, explosives,oil-well muds, and other mining applications. Plant parts other than thegrain of corn are also used in industry; for example, stalks and husksare made into paper and wallboard and cobs are used for fuel and to makecharcoal.

The goal of a corn breeder is to improve a corn plant's performance andtherefore, its economic value by combining various desirable traits intoa single plant. Improved performance is manifested in many ways. Higheryields of corn plants contribute to a more abundant food supply, a moreprofitable agriculture and a lower cost of food products for theconsumer. Improved quality makes corn kernels more nutritious. Improvedplant health increases the yield and quality of the plant and reducesthe need for application of protective chemicals. Adapting corn plantsto a wider range of production areas achieves improved yield andvegetative growth. Improved plant uniformity enhances the farmer'sability to mechanically harvest corn.

Natural, or open pollination, occurs in corn when wind blows pollen fromthe tassels to the silks that protrude from the tops of the ear shootand may include both self- and cross-pollination. Vigor is restored whentwo different inbred lines are cross-pollinated to produce the firstgeneration (F₁) progeny. A cross between two defined homozygous inbredcorn plants produce a uniform population of heterozygous hybrid cornplants and such hybrid corn plants are capable of being generatedindefinitely from the corresponding inbred seed supply.

When two different, unrelated inbred corn parent plants are crossed toproduce an F₁ hybrid, one inbred parent is designated as the male, orpollen parent, and the other inbred parent is designated as the female,or seed parent. Because corn plants are monoecious, hybrid seedproduction requires elimination or inactivation of pollen produced bythe female parent to render the female parent plant male sterile. Thisserves to prevent the inbred corn plant designated as the female fromself-pollinating.

The development of hybrid corn plants is a slow, costly process thatrequires the expertise of breeders and many other specialists. Thedevelopment of new hybrid corn varieties in a corn plant breedingprogram involves numerous steps, including: (1) selection of parent cornplants (germplasm) for initial breeding crosses; (2) inbreeding of theselected plants from the breeding crosses for several generations toproduce a series of inbred lines, which individually breed true and arehighly uniform; and, (3) crossing a selected inbred line with anunrelated line to produce the F₁ hybrid progeny having restored vigor.

Because hybrid corn varieties lose their commercial competitiveness overtime, a continuing need exists for novel hybrid corn varieties withimproved characteristics. The present invention addresses this need byproviding a novel hybrid corn variety designated 2643391 that possessesimproved performance relative to other hybrids in the same maturitygroups. To protect and to enhance yield production, trait technologiesand seed treatment options provide additional crop plan flexibility andcost effective control against insects, weeds and diseases, therebyfurther enhancing the potential of hybrid corn variety 2643391.

DETAILED DESCRIPTION OF THE INVENTION I. Definitions of PlantCharacteristics

In the description and examples that follow, a number of terms are used.To provide a clear and consistent understanding of the specification andclaims, including the scope to be given such terms, the followingdefinitions are provided.

Adjusted Test Weight: Weight of harvested grain in pounds per bushel ofNo. 2 yellow corn adjusted to 15.5% moisture according to the formula:(100%−actual moisture %)/(100%−15.5%)×(unadjusted weight of grain). Thestandard test weight of No. 2 yellow corn is 56 pounds per bushel.

Anther Color: Recorded at the time of pollen shed when anthers areactively dehiscing pollen as a standard color name [Light Green (1),Green-Yellow (5), Pale Yellow (6), Yellow (7), Salmon (9), Pink (11),Cherry Red (13), Purple (17), Tan (22)] and Munsell color code.

Cob Color: Recorded as a standard color name [Pink-Orange (10), Pink(11), Light Red (12), Cherry Red (13), Red (14), White (19)] and Munsellcolor code.

Dropped Ears: Actual number of dropped ears per plot detached from theplant that have fallen to the ground at harvest.

Ears Per Stalk: Number of ears with seed set on each plant.

Ear Height: Distance measured in centimeters from the ground to thehighest placed ear node (attachment point of the ear shank) of theuppermost developed ear on the stalk.

Ear Length: Length of an unhusked ear from the butt to the tip; measuredin centimeters.

Environments: Number of different geographic locations where two hybridsare grown together and in the same experiment.

50% Pollen (GDU from Planting): Number of GDUs after planting when 50%of the plants are shedding pollen.

50% Silk (GDU from Planting): Number of GDUs after emergence when 50% ofthe plants have extruded silk.

Genotype: Genetic constitution of a plant, plant part, or cell.

Glume Color: Color of the glume after exposure to sunlight and justbefore extruding anthers; recorded as a standard color name [Light Green(1), Medium Green (2), Dark Green (3), Very Dark Green (4), Green-Yellow(5), Salmon (9), Pink (11), Cherry Red (13), Red (14), Pale Purple (16)]and Munsell color code.

Kernel Type: Two of the common types for field corn are Flint and Dent;where Flint has mostly hard, glassy endosperm with smooth, hard seedcoats, and Dent has soft cores of starch that cause the end of thekernels to collapse or dent during drying.

Leaf Color: Color of the leaf; recorded as standard color name [LightGreen (1), Medium Green (2), Dark Green (3), Very Dark Green (4)] andMunsell color code.

Moisture: Actual percentage moisture of the grain at harvest.

Munsell Color Code: A system that describes colors based on threecharacteristics: hue, value (lightness), and chroma (color purity).

Number of Kernel Rows: Total number of kernel rows on the ear. If therows are indistinct, then this value is an average number of kernelslocated around the circumference of the ear at the mid-point of itslength.

Phenotype: Physical or external appearance of a plant or plant part.

Plant Height: Plant height in centimeters from the ground to the tip ofthe tassel.

Plots: Number of replicated plantings of a single hybrid that areharvested as data points for analyses in the same experiment.

Population: Number of seeds planted on a per acre basis.

Root Lodging: Percentage of corn plants that lean from the vertical axisat an approximate 30° angle or greater just before anthesis.

Silk Color: Color of the silk three days after its emergence; recordedas standard color name [Light Green (1), Green-Yellow (5), Pale Yellow(6), Yellow (7), Salmon (9), Pink-Orange (10), Pink (11), Cherry Red(13), Purple (17), Tan (22)] and Munsell color code.

Stalk Lodging: Percentage of plants that have broken over at or belowthe top ear node at harvest.

Standard Color Names: Color names include Light Green (1), Medium Green(2), Dark Green (3), Very Dark Green (4), Green-Yellow (5), Pale Yellow(6), Yellow (7), Yellow-Orange (8), Salmon (9), Pink-Orange (10), Pink(11), Light Red (12), Cherry Red (13), Red (14), Red and White (15),Pale Purple (16), Purple (17), Colorless (18), White (19), White Capped(20), Buff (21), Tan (22), Brown (23), Bronze (24), Variegated (25), andOther (26).

Tassel Type: The tassel branch shape recorded as erect or spreading. Theangle of the base of each tassel branch is used to indicate thedirection of the branches. Erect longer or lighter tassels that droopover on the tip are classified as erect.

Yield: Yield of grain at harvest in bushels per acre adjusted to 15.0%moisture according to the formula: [(100−% grainmoisture)×109.815×weights (lbs)]/row length (feet)/row width (inches)/(#of harvest rows).

II. Hybrid Corn Variety 2643391 A. Hybrid Corn Variety 2643391

In accordance with one aspect of the present invention, provided is anew yellow dent hybrid corn variety and plants thereof designated2643391. Hybrid variety 2643391 was produced from a cross of the inbredvarieties designated SLA21 and XHB03. The inbred parents have beenself-pollinated and ear-rowed a sufficient number of generations withcareful attention paid to uniformity of plant type to show uniformityand stability within the limits of environmental influence. Adescription of physiological and morphological characteristics of hybridcorn variety 2643391 is presented in Table 1. It should be noted thatthese characteristics may have been measured on a trait bearing versionof hybrid corn variety 2643391. However, one of ordinary skill in cornbreeding art would recognize that the measured characteristics would berepresentative of either the non-trait bearing version or atrait-bearing versions.

TABLE 1 Physiological and Morphological Characteristics of 2643391Characteristic Value STALK Plant Height (cm) 251.50 Ear Height (cm)124.50 LEAF Leaf Color (standard) Dark Green (03) TASSEL 50% Pollen (GDUfrom Planting) 1435 Tassel Type (Spreading, Erect) Erect Anther Color(standard) Yellow (07) Glume Color (standard) Medium Green (02) EAR 50%Silk (GDU from Planting) 1435 Silk Color (standard) Yellow-Orange (08)Ears Per Stalk (count) 1 Ear Length (cm) 20 Number of Kernel Rows(count) 16-20 Cob Color (standard) Red (14) KERNEL Type (Flint, Dent)Dent

It should be appreciated by one having ordinary skill in the art that,for the quantitative characteristics identified in Table 1, the valuespresented are typical values. These values may vary due to theenvironment and accordingly, other values that are substantiallyequivalent are also within the scope of the invention.

The present invention also relates to one or more corn plant parts ofhybrid corn variety 2643391. Corn plant parts include plant cells, plantprotoplasts, plant cell tissue cultures from which corn plants can beregenerated, plant DNA, plant calli, plant clumps, and plant cells thatare intact in plants or parts of plants, such as embryos, pollen,ovules, flowers, seeds, kernels, ears, cobs, leaves, husks, stalks,roots, root tips, brace roots, lateral tassel branches, anthers,tassels, glumes, silks, tillers, and the like.

B. Hybrid Corn Variety Seed Designated 2643391

A corn kernel is composed of four structural parts: (1) the pericarp,which is a protective outer covering (also known as bran or hull); (2)the germ (also known as an embryo); (3) the endosperm; and, (4) the tipcap, which is the point of attachment to the cob. Another aspect of thepresent invention is one or more parts of hybrid corn variety seed2643391, such as the pericarp or the germ and/or the endosperm whichremain upon removal of the pericarp and adhering remnants of the seedcoat.

Corn yield is affected by the conditions to which seeds and seedlings(young plants grown from seeds) are exposed. Seeds and seedlings may beexposed to one of, or a combination of, for example, cold, drought,salt, heat, pollutants, and disease, all of which are conditions thatpotentially retard or prevent the growth of crops therefrom. Forexample, temperature extremes are typical in the upper Midwest region ofthe United States. Furthermore, diseases evolved from pathogens anddeterioration caused by fungi are potentially harmful to seeds andseedlings. Thus, it is desirable to treat seeds as by coating orimpregnating the seeds with compositions that render the seeds andseedlings grown therefrom more hardy when exposed to such adverseconditions.

Accordingly, another aspect of the present invention relates to a coatedand/or impregnated seed of hybrid corn variety designated 2643391 and tocoated and/or impregnated seed derived therefrom. Various agents havebeen used to treat seeds to increase resistance of the plants tostressed conditions, such as cold, drought, salt, and fungi. Such agentsinclude, for example, sodium methylphenyl-pentadienate, trichloroaceticacid, polyoxyalkylene-organo-siloxane block copolymer, 5-aminolevulinicacid, salicylic acid, thiamethoxam, potassium chloride, and polyvinylalcohol and are useful alone, or in combination in the presentinvention.

C. Deposit Information

A deposit of at least 2500 seeds of inbred parent plant varieties SLA21(U.S. Pat. No. 8,404,954 issued Mar. 26, 2013, the entire disclosure ofwhich is incorporated herein by reference) and XHB03 (U.S. applicationSer. No. 13/495,036 filed Jun. 13, 2012, the entire disclosure of whichis incorporated herein by reference) has been made with the AmericanType Culture Collection (ATCC), 10801 University Boulevard, Manassas,Va. 20110-2209 USA, and assigned ATCC Accession Nos. PTA-10335, andPTA-12595, respectively. The seeds were deposited with the ATCC on Sep.11, 2009, and Feb. 23, 2012, respectively. Access to this deposit willbe available during the pendency of the application to the Commissionerof Patents and Trademarks and persons determined by the Commissioner tobe entitled thereto upon request. The deposits will be maintained in theATCC Depository, which is a public depository, for a period of 30 years,or 5 years after the most recent request, or for the enforceable life ofthe patent, whichever is longer, and will be replaced if it becomesnonviable during that period. Applicant does not waive any infringementof their rights granted under this patent or under the Plant VarietyProtection Act (7 U.S.C. 2321 et seq.).

III. Processes of Preparing Novel Corn Plants A. Novel Inbred PlantsObtained from Hybrid Corn Variety 2643391

In accordance with processes of the present invention, hybrid cornvariety 2643391 is crossed with itself or any different corn plant suchas an inbred corn plant or a hybrid corn plant to develop a novel inbredline. For example, hybrid corn variety 2643391 may be inbred, i.e.,crossed to itself or sib-pollinated, and the resulting progeny eachselfed for about 5 to about 7 or more generations, thereby providing aset of distinct, pure-breeding inbred lines wherein each of the linesreceived all of its alleles from the hybrid corn plant. Double haploidmethods can also be used to obtain an inbred corn plant that ishomozygous at essentially every locus, wherein the inbred corn plantreceived all of its alleles from the hybrid corn plant. In otherembodiments, hybrid corn variety 2643391 is crossed with a differentcorn plant that may include any inbred corn plant, another germplasmsource, a haploid or mutation inducing stock, or a trait donor plant,thereby providing a set of distinct, pure-breeding inbred lines. Theresulting inbred lines could then be crossed with other inbred ornon-inbred lines and the resulting inbred progeny analyzed forbeneficial characteristics. In this way, novel inbred lines conferringdesirable characteristics could be identified.

IV. Novel Hybrid Plants A. Novel Hybrid Seeds and Plants

In yet another aspect of the invention, processes are provided forproducing hybrid corn variety 2643391, which processes generallycomprise crossing a first parent corn plant SLA21 with a second parentcorn plant XHB03. In these processes, crossing will result in theproduction of seed. The seed production occurs regardless whether theseed is collected.

Any time the inbred corn plant SLA21 is crossed with another, differentcorn inbred plant XHB03, a first generation (F₁) corn hybrid variety2643391 plant is produced. Therefore, any F₁ hybrid corn plant or cornseed which is produced with these two parent corn lines is part of thepresent invention.

In embodiments of the present invention, the first step of “crossing”the first and the second parent corn plants comprises planting,preferably in pollinating proximity, seeds of a first inbred corn plantand a second, distinct inbred corn plant. As discussed herein, the seedsof the first inbred corn plant and/or the second inbred corn plant canbe treated with compositions that render the seeds and seedlings growntherefrom more hardy when exposed to adverse conditions.

A further step comprises cultivating or growing the seeds of the firstand second parent corn plants into plants that bear flowers. If theparental plants differ in timing of sexual maturity, techniques may beemployed to obtain an appropriate nick, i.e., to ensure the availabilityof pollen from the parent corn plant designated the male during the timeat which silks on the parent corn plant designated the female arereceptive to the pollen. Methods that may be employed to obtain thedesired nick include delaying the flowering of the faster maturingplant, such as, but not limited to delaying the planting of the fastermaturing seed, cutting or burning the top leaves of the faster maturingplant (without killing the plant) or speeding up the flowering of theslower maturing plant, such as by covering the slower maturing plantwith film designed to speed germination and growth or by cutting the tipof a young ear shoot to expose silk.

In a preferred embodiment, the corn plants are treated with one or moreagricultural chemicals as considered appropriate by the grower.

A subsequent step comprises preventing self-pollination orsib-pollination of the plants, i.e., preventing the silks of a plantfrom being fertilized by any plant of the same variety, including thesame plant. This is preferably done in large scale production bycontrolling the male fertility, e.g., treating the flowers so as toprevent pollen production or alternatively, using as the female parent amale sterile plant of the first or second parent corn plant (i.e.,treating or manipulating the flowers so as to prevent pollen production,to produce an emasculated parent corn plant or using as a female, acytoplasmic male sterile version of the corn plant). This control mayalso be accomplished in large scale production by physical removal ofthe tassel from the female plant, either by pulling the tassel by hand,cutting with a rotary cutter, or pulling with a mechanical tasselpulling machine. In small scale production, corn breeder's shoot bags,usually plastic or glassine, applied to cover the ear shoot prior to theextrusion of silks provide effective control of unwantedself-pollination or sib-pollination.

Yet another step comprises allowing cross-pollination to occur betweenthe first and second parent corn plants. When the plants are not inpollinating proximity, this is done by placing a bag, usually paper,over the tassels of the first plant and another shoot bag over the earshoot, prior to the extrusion of silk, of the incipient ear on thesecond plant. The bags are left in place usually overnight. Since pollenstops shedding each day and loses viability and new pollen is shed eachmorning, this assures that the silks are not pollinated from otherpollen sources, that any stray pollen on the tassels of the first plantis dead, and that the only pollen transferred comes from the firstplant. The pollen bag over the tassel of the first plant is then shakenvigorously to enhance release of pollen from the tassels and removedfrom the first plant. Finally, in one continuous motion, the shoot bagis removed from the silks of the incipient ear on the second plant, andthe pollen bag containing the captured pollen is placed over the silksof the incipient ear of the second plant, shaken again to disperse thecaptured pollen, and left in place covering the developing ear toprevent contamination from any unwanted fresh airborne pollen. In largescale production, crossing is accomplished by isolated open-pollinatedcrossing fields whereby corn plants of the parent designated as thefemale, which are controlled for male fertility, are allowed to bepollinated by other plants of a different corn type where such plantsare adjacent to the plants designated as the female parent.

A further step comprises harvesting the seeds, near or at maturity, fromthe ear of the plant that received the pollen. In a particularembodiment, seed is harvested from the female parent plant, and whendesired, the harvested seed can be grown to produce a first generation(F₁) hybrid corn plant.

Yet another step comprises drying and conditioning the seeds, includingthe treating, sizing (or grading) of seeds, and packaging for sale togrowers for the production of grain or forage. As with inbred seed, itmay be desirable to treat hybrid seeds with compositions that render theseeds and seedlings grown therefrom more hardy when exposed to adverseconditions. Mention should be made that resulting hybrid seed is sold togrowers for the production of grain and forage and not for breeding orseed production.

Still further, the present invention provides a hybrid corn plantproduced by growing the harvested seeds produced on the male-sterileplant as well as grain produced by the hybrid corn plant.

A single cross hybrid is produced when two different inbred parent cornplants are crossed to produce first generation F₁ hybrid progeny.Generally, each inbred parent corn plant has a genotype whichcomplements the genotype of the other inbred parent. Typically, the F₁progeny are more vigorous then the respective inbred parent corn plants.This hybrid vigor, or heterosis, is manifested in many polygenic traits,including markedly improved yields and improved stalks, roots,uniformity and insect and disease resistance. It is for this reason thatsingle cross F₁ hybrids are generally the most sought after hybrid. Athree-way, or modified single-cross hybrid is produced from three inbredlines (or synthetics) where two of the inbred lines are crossed (A×B)and then the resulting F₁ hybrid is crossed with the third inbred(A×B)×C, as where a modified female is used in the cross. A modifiedfemale provides an advantage of improved seed parent yield whereas amodified male improves pollen flow. A double cross hybrid is producedfrom four inbred lines crossed in pairs (A×B and C×D), thereby resultingin two F₁ hybrids that are crossed again. Double cross hybrids are morecommon in countries wherein less demand exists for higher yieldingsingle cross hybrids. Synthetic populations or crosses are developed bycrossing two or more inbred lines (or hybrids, or germplasm sources)together and then employing one of many possible techniques to randommate the progeny. Random mating the progeny is any process used by plantbreeders to make a series of crosses that will create a new germplasmpool from which new breeding lines can be derived. Much of the hybridvigor exhibited by F₁ hybrids is lost in the next generation (F₂).Consequently, seed from hybrids are not typically used for plantingstock.

B. Physical Description of F₁ Hybrids and F₁ Hybrid Comparison

During the development of a hybrid plant detailed evaluations of thephenotype are made including formal comparisons with other commerciallysuccessful hybrids. Because the corn is grown in close proximity,environmental factors that affect gene expression, such as moisture,temperature, sunlight, and pests, are minimized. For a decision to bemade to commercialize a hybrid, it is not necessary that the hybrid bebetter than all other hybrids. Rather, significant improvements must beshown in at least some traits that would create improvements in someniches. Examples of such comparative performance data for the hybridcorn plant 2643391 are set forth herein below in Table 2.

TABLE 2 Hybrid 2643391 Compared With Other Commercial Hybrids MycogenMycogen Characteristic 2643391 2K594 2J597 Yield (bu/ac) 210.93 200.76190.37 Moisture (%) 18.20 18.61 19.27 Stalk Lodging (%) 4.66 4.54 3.56Root Lodging (%) 2.56 2.87 3.76 Adjusted Test 55.62 56.28 56.43 Weight(lbs/bu) Population 32,480 33,500 32,460 (plants/ac) Plant Height (cm)251.50 251.50 241.30 Ear Height (cm) 124.50 132.10 129.50 Dropped Ears 122 0 (count) Environments 45 47 62 (count) Plots/mean (count) 45 47 62

V. Novel 2643391-Derived Plants

All plants produced using hybrid corn variety 2643391 as a parent arewithin the scope of this invention. This includes plants essentiallyderived with the term “essentially derived variety” having the meaningascribed to such term in 7 U.S.C. §2104(a)(3) of the Plant VarietyProtection Act, which definition is hereby incorporated by reference.This also includes progeny plant and parts thereof with at least oneancestor that is hybrid corn variety 2643391 and more specifically wherethe pedigree of this progeny includes 1, 2, 3, 4, and/or 5 or crosspollinations to hybrid corn variety 2643391, or a plant that has 2643391as a progenitor. All breeders of ordinary skill in the art maintainpedigree records of their breeding programs. These pedigree recordscontain a detailed description of the breeding process, including alisting of all parental lines used in the breeding process andinformation on how such line was used. Thus, a breeder would know if2643391 were used in the development of a progeny line, and would alsoknow how many breeding crosses to a line other than 2643391 were made inthe development of any progeny line. A progeny line so developed maythen be used in crosses with other, different, corn inbreds to producefirst generation F₁ corn hybrid seeds and plants with superiorcharacteristics.

Accordingly, another aspect of the present invention is methods forproducing an inbred corn line 2643391-derived corn plant. This methodfor producing a 2643391-derived corn plant, comprises: (a) crossinghybrid corn variety 2643391 with a second corn plant to yield progenycorn seed; and, (b) growing the progeny corn seed, (under plant growthconditions), to yield the 2643391-derived corn plant. Such methods mayfurther comprise the steps of: (c) crossing the 2643391-derived cornplant with itself or another corn plant to yield additional2643391-derived progeny corn seed; (b) growing the progeny corn seed ofstep (d) (under plant growing conditions), to yield additional2643391-derived corn plants; and (e) repeating the crossing and growingsteps of (c) and (d) from 0 to 7 times to generate further2643391-derived corn plants. Still further, this may comprise utilizingmethods of haploid breeding and plant tissue culture methods to deriveprogeny of the 2643391-derived corn plant.

VI. Corn Transformation

With the advent of molecular biological techniques that have allowed theisolation and characterization of genes that encode specific proteinproducts, scientists in the field of plant biology developed a stronginterest in engineering the genome of plants to contain and to expressforeign genes, or additional, or modified versions of native orendogenous genes (perhaps driven by different promoters) to alter thetraits of a plant in a specific manner. Such foreign, additional and/ormodified genes are referred to herein collectively as “transgenes.” Thepresent invention, in particular embodiments, also relates totransformed versions of the claimed hybrid corn variety 2643391containing one or more transgenes.

Backcrossing methods can be used with the present invention to improveor introduce a trait in a hybrid via modification of its inbredparent(s). The term backcrossing as used herein refers to the repeatedcrossing of a hybrid progeny back to one of the parental corn plants forthat hybrid. The parental corn plant which contributes the locus or locifor the desired trait is termed the nonrecurrent or donor parent. Thisterminology refers to the fact that the nonrecurrent parent is used onetime in the backcross protocol and therefore does not recur. Theparental corn plant to which the locus or loci from the nonrecurrentparent are transferred is known as the recurrent parent as it is usedfor several rounds in the backcrossing protocol (Poehlman et al., 1995;Fehr, 1987; Sprague and Dudley, 1988).

In a typical backcross protocol, the original parent hybrid of interest(recurrent parent) is crossed to a second variety (nonrecurrent parent)that carries the genetic locus of interest to be transferred. Theresulting progeny from this cross are then crossed again to therecurrent parent and the process is repeated until a corn plant isobtained wherein essentially all of the desired morphological andphysiological characteristics of the recurrent parent are recovered inthe converted plant, in addition to the transferred locus from thenonrecurrent parent. The backcross process may be accelerated by the useof genetic markers, such as SSR, RFLP, SNP or AFLP markers to identifyplants with the greatest genetic complement from the recurrent parent.

The selection of a suitable recurrent parent is an important step for asuccessful backcrossing procedure. The goal of a backcross protocol isto add or substitute one or more new traits in the original inbred andhybrid progeny therefrom. To accomplish this, a genetic locus of therecurrent parent is modified or substituted with the desired locus fromthe nonrecurrent parent, while retaining essentially all of the rest ofthe desired genetic, and therefore the desired physiological andmorphological constitution of the original plant. The choice of theparticular nonrecurrent parent will depend on the purpose of thebackcross; one of the major purposes is to add some commerciallydesirable, agronomically important trait to the plant. The exactbackcrossing protocol will depend on the characteristic or trait beingaltered to determine an appropriate testing protocol. Althoughbackcrossing methods are simplified when the characteristic beingtransferred is a dominant allele, a recessive allele may also betransferred. In this instance it may be necessary to introduce a test ofthe progeny to determine if the desired characteristic has beensuccessfully transferred.

Many traits have been identified that are not regularly selected for inthe development of a new variety but that can be improved bybackcrossing techniques. A genetic locus conferring the traits may ormay not be transgenic. Examples of such traits known to those of skillin the art include, but are not limited to, male sterility, waxy starch,herbicide resistance, resistance for bacterial, fungal, or viraldisease, insect resistance, male fertility and enhanced nutritionalquality. These genes are generally inherited through the nucleus, butmay be inherited through the cytoplasm. Some known exceptions to thisare genes for male sterility, some of which are inheritedcytoplasmically, but still act as a single locus trait.

Direct selection may be applied where a genetic locus acts as a dominanttrait. An example of a dominant trait is the herbicide resistance trait.For this selection process, the progeny of the initial cross are sprayedwith the herbicide before the backcrossing. The spraying eliminates anyplants which do not have the desired herbicide resistancecharacteristic, and only those plants which have the herbicideresistance gene are used in the subsequent backcross. This process isthen repeated for all additional backcross generations.

It is understood to those of skill in the art that a transgene need notbe directly transformed into a plant, as techniques for the productionof stably transformed corn plants that pass single loci to progeny byMendelian inheritance is well known in the art. Such loci may thereforebe passed from parent plant to progeny plants by standard plant breedingtechniques that are well known in the art.

All publications, patents and patent applications mentioned in thespecification are indicative of the level of those skilled in the art towhich this invention pertains. All such publications, patents and patentapplications are incorporated by reference herein to the same extent asif each was specifically and individually indicated to be incorporatedby reference herein.

The foregoing invention has been described in some detail by way ofillustration and example for purposes of clarity and understanding.However, it should be appreciated by those having ordinary skill in theart that certain changes and modifications such as single genemodifications and mutations, somoclonal variants, variant individualsselected from large populations of the plants of the instant inbred andthe like may be practiced within the scope of the invention, as limitedonly by the scope of the appended claims, without departing from thetrue concept, spirit, and scope of the invention.

What is claimed is:
 1. A seed of the hybrid corn variety 2643391,produced by crossing a first plant of variety SLA21 with a second plantof variety XHB03, wherein representative seed of said varieties SLA21and XHB03 have been deposited under ATCC Accession numbers PTA-10335 andPTA-12595, respectively.
 2. A plant of the hybrid corn variety 2643391produced by growing the seed of claim
 1. 3. A plant part of the plant ofclaim
 2. 4. A method of producing hybrid corn seed, said methodcomprising crossing a plant of variety SLA21 with a plant of varietyXHB03, wherein representative seed of variety SLA21 and variety XHB03have been deposited under ATCC Accession numbers PTA-10335 andPTA-12595, respectively.
 5. A method for producing corn grain, saidmethod comprising growing the plant of claim 2 until grain is producedand collecting the grain.
 6. A method of producing a corn plant derivedfrom the hybrid corn variety 2643391, said method comprising crossingthe plant of claim 2 with a second corn plant to produce a progeny cornplant derived from the hybrid corn variety
 2643391. 7. A seed of thehybrid corn variety 2643391, produced by crossing a first plant ofvariety SLA21 with a second plant of variety XHB03, whereinrepresentative seed of said varieties SLA21 and XHB03 have beendeposited under ATCC Accession numbers PTA-10335 and PTA-12595,respectively; and wherein at least one of the varieties, SLA21 andXHB03, further comprises a locus conversion and wherein said hybrid seedproduces a plant having the same phenotypic traits listed in Table 1 for2643391 when grown under the same environmental conditions.
 8. The seedof the hybrid corn variety 2643391 of claim 7, wherein the locusconversion confers a trait selected from the group consisting of malesterility, herbicide tolerance, insect resistance, disease resistance,modified fatty acid metabolism, modified phytic acid metabolism,modified carbohydrate metabolism and modified protein metabolism.